a(n) = (15^n - (-2)^n)/17.

Terms

a(0) =0a(1) =1a(2) =13a(3) =199a(4) =2977a(5) =44671a(6) =670033a(7) =10050559a(8) =150758257a(9) =2261374111a(10) =33920611153a(11) =508809168319